The prevalence of electric vehicles is set to increase considerably in the near future. With the prevalence of electric vehicles, new requirements are set for the supply infrastructure. Electric vehicles do not only have to be able to be supplied with electrical energy in the domestic field but also outside the domestic field. To this end, charging stations should be made available in public places, where users of electric vehicles may obtain electrical energy. The charging stations may, for example, be arranged in public parking areas, in car parks or even in private parking areas, for example in the region of the workplace of the user. Users of electric vehicles could then connect their vehicles to such charging stations. During their absence, the battery of the electric vehicles may be charged up.
A drawback with the use of stationary charging stations which are accessible in public areas is, however, that the structure of the electric vehicles is heterogenous, which means that very different electric vehicles are operated by very different plugs and plug systems.
The use of the respective plug and/or plug system substantially depends on the type of charging process desired. Thus, firstly a differentiation is made between the duration of the charging process: during a normal charging process, which lasts over a lengthy time period with a low to moderate charging current, charging cables known from the domestic field with a small or medium cable cross section are able to be used. During a rapid charging process, which takes place within a shorter time at a higher amperage, charging cables with a correspondingly larger cross section are required. For example, charging cables with a cable cross section of 6 mm2 are able to be used for a maximum of 32 A, whilst such charging cables with a cross section of 16 mm2, as used in rapid charging stations, are acceptable for amperages of up to 63 A.
Also a differentiation is made in the type of cable connection: the electric vehicle may be connected to the AC power supply system in the charging station, either by using a charging cable and a plug which are permanently connected to the electric vehicle, or by using a releasable cable accessory with cable connectors to the electric vehicle and to the charging station.
Generally, a conventional connection or extension cable has a plug on the one side and a coupling on its other side. Cable systems which are primarily used in the industrial field or with higher power consumers in the domestic field, are known as so-called CEE-plug connectors and exist in many variants. They are designed so that in each case the plug of one type only fits into the jack and/or socket of the same type. Thus the nature and diameter of the respective connector are dependent on the current carrying capacity, a difference being made between the amperages 16 A, 32 A, 63 A and 125 A. In the known CEE-system, it is not possible to connect plugs and sockets of different amperages to one another. In these plug connection systems, only the couplings are regarded as current conducting components and accordingly only the contacts of the couplings are designed to be insulated so that they are shockproof.
Such known CEE-plug connectors are, however, not suitable in connection with charging electric vehicles. One reason is that not only is energy able to be stored in the battery of the electric vehicle but, on the other hand, it is intended that energy is able to be transferred back from the electric vehicle to the charging station. Thus in such charging cables it is necessary that both the contacts in the coupling and the contacts in the plug are insulated so that they are shockproof. Alternatively, it is also possible to use a charging cable with two plugs.
In order to ensure a corresponding universality of the connection options, therefore, in electric vehicles the known grading of the plug and/or coupling sizes differs according to the permissible amperages, in which a small plug size corresponds to an amperage of 16 A, a medium plug size corresponds to an amperage of 32 A and a large plug size corresponds to an amperage of 63 A.
Instead, it is desirable that an electric vehicle is able to be connected by the same charging cable to a plug socket in the charging station, irrespective of how high the respective charging current is. The use of a single size for the plug connector of a charging cable, however, requires an indication of the maximum permissible amperage for the charging cable and/or the plug connector, in order to avoid overload. It is known, for such an indication, to carry out a so-called “coding” of the maximum amperage, in which an ohmic resistor is arranged within the housing of the plug connector. Different resistance values are used for different permissible amperages. At the connection of the plug connector to the electric vehicle and/or to the charging station, the value of the ohmic resistor of the respective location is determined, and the value of the maximum permissible amperage of the charging cable detected therefrom. With the knowledge of the maximum charging current to be produced by the charging station and also taking into account the amount of energy required by the electric vehicle, a synchronisation then takes place by the optimal charging current under the given conditions being set, said charging current being determined by the weakest link in the chain of the total charging circuit.
However, the disclosed coding of the maximum permissible amperage of the charging cable has the drawback that only specific discrete numerical values of the amperage may be predetermined. In the case of a deterioration of contacts by ageing processes or corrosion of the plug connector, which lead to increased resistance in the region of the plug connector, therefore, a risk of accident occurs, up to and including the combustion of the plug connection. The primary cause is that by the greater heat losses in the region of the deteriorated contact connection, an impermissible temperature increase occurs, when a charging current is used which corresponds to the predetermined fixed coding value.
The object of the present invention is to improve a device and/or a system of the aforementioned type so that greater safety may be achieved against the disclosed thermal risks.